The present invention relates to a high-pressure discharge lamp in which the internal pressure is 1 atmospheric pressure or more during operation and a method for producing the same.
FIG. 14 shows an example of the configuration of a conventional high-pressure discharge lamp. The high-pressure discharge lamp shown in FIG. 14 includes an arc tube (bulb) portion 50 and side tube portions 51 extending from the arc tube portion 50. The heads of electrode rods 52 are positioned inside the arc tube portion 50, and a part of the electrode rods 52, metal foils 53 whose first ends are electrically connected to the electrode rods 52, and a part of external lead wires 54 electrically connected to the other (second) ends of the metal foils 53 are provided in the side tube portions 51.
Mercury and metal halide, which are luminous species 56, are enclosed in the arc tube portion 50. The electrode rods 52 are substantially made of tungsten, and the side tube portions 51 are substantially made of quartz glass. The coefficient of thermal expansion of tungsten of the electrode rods 52 is different from that of quartz glass of the side tube portions 51, so that it is difficult for these two materials to be hermetically attached. Therefore, the tungsten is hermetically attached to the quartz glass by plastically deforming the thin metal foils 53, thus maintaining the airtightness in the arc tube portion 50.
Although it appears that the electrode rods 52 and the side tube portions 51 are hermetically attached, in reality, very small gaps 55 are present. It is known that the luminous species 56 enters the gap 55 while the lamp is repeatedly turned on and off. The temperature of these significantly small gaps 55 is lower than that of the arc tube portion 50 during lamp operation, so that the luminous species 56 hardly evaporates again to return to the arc tube portion 50. As a result, the luminous species 56 present in the arc tube portion 50 is decreased so that proper emission cannot be obtained. Furthermore, when the luminous species 56 reaches the metal foils 53 through the gaps 55, the metal foils 53 may be detached from the side tube portions 51, which may cause leaks in the arc tube portion 50 and thus the life of the lamp may be shortened.
Conventionally, there have been attempts to solve this problem. For example, Japanese Laid-Open Patent Publication No. 10-269941 discloses a technique of attaching tungsten coils to the electrode rods. In this technique, the coils are formed in a pitch that does not allow melted quartz glass to go into the coil pitch at the time of sealing. This publication describes that by performing sealing while stretching the coils to the discharge end side of the electrode rods, no gap that might accommodate the luminous materials such as metal halide and mercury is formed in portions of the electrode rods near the metal foils. More sepcifically, when sealing is performed while stretching the coils to the discharge end side, the coils are extended. Therefore, the inner diameter of the coils near the metal foils becomes small so that the coils are in contact with the outer surface of the electrode rods. In addition, the coil pitch is increased, so that melted quartz glass enters between the coils. As a result, the quartz glass becomes in contact with the outer surface of the electrode rods, so that the gap to which otherwise the luminous material might enter is filled.
However, although the gap to which the luminous materials might enter can be filled, the method of this publication has the following problem. Since this method fails to take the difference in the coefficient of the thermal expansion between tungsten and quartz glass, the lamp is broken after repetitive operation of on and off of the lamp because of failure of absorption of the difference in the coefficient of thermal expansion. In the above method, since the coils are wound tightly around the electrode rods, the coils cannot be plastically deformed, unlike the thin metal foils. In this state, when the lamp is operated, the electrode rods expand because of Joule heat, and this force presses quartz glass to the point where the lamp is broken. That is to say, the method of this publication is not practical in the lamp that is required to turn on and off repeatedly.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide a high-pressure discharge lamp having a long life and a method for producing the same.
A high-pressure discharge lamp of the present invention includes an arc tube portion enclosing a luminous material in the tube; a side tube portion substantially made of quartz glass that extends from the arc tube portion; and an electrode rod whose first end is arranged in the arc tube portion and a part of which is provided in the side tube portion, wherein the electrode rod is substantially made of tungsten, and a region containing at least one of copper oxide and copper is present in at least a part of the portion of the side tube portion in which the part of the electrode rod is positioned.
It is preferable that the side tube portion in the region is made of the at least one of copper oxide and copper, Vycor glass, and quartz glass.
It is preferable that the at least one of copper oxide and copper is contained in an amount of 1% by weight to 30% by weight in the side tube portion in the region.
It is preferable that the high-pressure discharge lamp further includes a metal foil electrically connected to a second end of the electrode rod and provided in the side tube portion, wherein the metal foil is electrically connected to an external lead wire.
In one embodiment of the present invention, the side tube portion in the region and the electrode rod are attached tightly to each other, and at least a part of the side tube portion other than the region and the metal foil are attached tightly to each other.
It is preferable that the region is present on the metal foil side from the center between an end of the arc tube portion that is a border with the side tube portion and an end of the metal foil that is connected to the electrode rod.
It is preferable that the diameter of the electrode rod is 0.3 mm or less.
In one embodiment of the present invention, at least metal halide is enclosed in the arc tube portion as the luminous material.
In one embodiment of the present invention, the metal halide includes a halide of indium.
According to another aspect of the present invention, a method for producing a high-pressure discharge lamp includes the steps of: (a) preparing a glass tube including an arc tube portion, a side tube portion extending from the arc tube portion, and substantially made of quartz glass; (b) passing an electrode rod substantially made of tungsten through a cylindrical structure containing at least one of copper oxide and copper; (c) inserting the electrode rod into the side tube portion such that a first end of the electrode rod is positioned in the arc tube portion; and (d) forming a region containing the at least one of copper oxide and copper in the side tube portion by heating the cylindrical structure and the side tube portion for tight attachment.
In one embodiment of the present invention, the cylindrical structure in the step (b) is a glass cylinder made of the at least one of copper oxide and copper, Vycor glass and quartz glass.
In one embodiment of the present invention, the cylindrical structure in the step (b) is obtained by adhering glass powder containing at least one of copper oxide powder and copper powder to a glass sleeve made of Vycor glass.
It is preferable that in the step (b), the electrode rod, which is connected to a metal foil at a second end of the rod, is passed through the cylindrical structure such that at least a part of the metal foil is covered with the cylindrical structure.
It is preferable that in the step (c), the electrode rod is inserted into the side tube portion such that the cylindrical structure is arranged on the metal foil side from the center between an end of the arc tube portion that is a border with the side tube portion and an end of the metal foil that is connected to the electrode rod.
In the present invention, a region including at least one of copper oxide or copper is present in at least a part of the portion of a side tube portion in which a part of the electrode rod is positioned. Therefore, the side tube portion positioned in that region and the electrode rod are tightly attached satisfactorily. This prevents the enclosed luminous species from entering into a small gap between the electrode rod and the side tube portion. As a result, leaks in the arc tube portion caused by the detachment of the metal foil from the side tube portion can be prevented. Furthermore, since leaks in the arc tube portion are prevented by tight attachment between the side tube portion positioned in that region and the electrode rod, a high-pressure discharge lamp can be provided, that is not broken even if the lamp is turned on and off repeatedly and thus has a long life.
According to the present invention, since a region containing at least one of copper oxide and copper is present in at least a part of the portion of a side tube portion in which a part of an electrode rod is positioned, the lamp life of a high-pressure discharge lamp can be improved.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.